Induction of triploids through sexual polyploidisation requires in-depth understanding of plant reproductive biology. However, the method to identify the developmental stages of the gametes in Eucalyptus is still unclear. In this study, microsporogenesis and megasporogenesis of Eucalyptus pellita were revealed by staining with acetocarmine and paraffin sectioning. Results showed two types of stamens existed in a single flower, and the microsporogenesis in anthers of long stamens were significantly ahead of those in short ones. A temporal relationship between megasporogenesis and microsporogenesis could be found in a single flower where megasporogenesis was consistent with microsporogenesis in the long stamens. Although the flower bud development and meiosis process of a single flower bud at different positions on the branch were asynchronous, those positioned at the upper end of the branch were relatively consistent. From the study report, a simple and accurate method to identify the meiotic period of megasporocytes was proposed based on temporal relationships between megasporogenesis and microsporogenesis. The study not only deepened the understanding of E. pellita reproductive biology, but also provided important theoretical guidance for the genetic improvement of this tree species, especially the triploid breeding by sexual polyploidisation.

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